Yes, you can use pedalSHIELD with a base guitar by changing (C1 C4 C6 C7 C10 C11) from 0.1uF to 0.5uF (0.47nF), they change the high pass filters allowing more low harmonics to to through the pedal, the rest of the pedal will work the same.
In the current design there are several high pass filters that attenuate the excess of bass. The cut frequency is defined by R= 100K and C=100nF and freqs below 15.9 Hz are attenuated.
Using R=100K and C= 470nF only freqs below 4Hz get attenuation, you can use
any onlnie high pass filter calculator to make the numbers.
Any film/ceramic cap will do,take care cause they tend to be a bit bulky... you can check this from mouser:
SR215E474MAR
Also what the modifications could you add onto the pedal to change or alternate the design as an experiment?
The
MXR Micro Amp (and MXR Distortion+) are not far from the input stage circuit. I am sure you can modify the pedal to be fully analogue and sound like one of those.